1. Field of the Invention
The present invention relates to an actuator and, more particularly, to an actuator for use in changing the cross-sectional area of an oil passage in a shock absorber of a variable damping force suspension system.
2. Description of the Related Art
FIG. 1 is a sectional side elevational view of a conventional actuator of the kind described, while FIG. 2 is a sectional view taken along the line II--II of FIG. 1. The actuator has a housing 1 provided at its one side with an opening, and an annular permanent magnet 2 rotatably mounted in the housing 1. An output shaft 4 is received in the center of a yoke 3 which is fixed to the inner periphery of the permanent magnet 2. A pin 5 fixed to the output shaft 4 engages with a groove 3a formed in the yoke 3. A stator 6, which surrounds the permanent magnet 2, is provided on its inner peripheral surface with projecting poles 6a to 6f opposing the permanent magnet 2. Coils 7a to 7f are wound on the projecting poles 6a to 6f, respectively. Terminals 8a to 8d are connected to the coils 6a to 6f and also to lead wires 9a to 9c. The opening in the housing 1 is covered by a cover 10. A rubber cap 11 covers the housing 1 together with the cover 10. One end of a shock absorber 12 abuts the actuator through a rubber ring 13.
In this actuator, the stator 6 is press-fitted in the housing 1, while the permanent magnet 2 and the yoke 3 are rotatably mounted. The rotation of the permanent magnet 2 and the yoke 3 is transmitted to the output shaft 4 through the pin 5 which engages with the groove 3a formed in the yoke 3. The permanent magnet 2 and, hence, the yoke 3, as well as the output 4, are prevented from moving axially by the cover 10. The lead wires 9a to 9c connected to the terminals 8a to 8c are led to the exterior through holes 11a to 11c which are formed in the rubber cap 11. The juncture between the housing 1 and the cover 10 is covered by the rubber cap 11 which prevents water droplets from coming into the juncture. Invasion of water droplets from the lower side is also prevented by the fact that the shock absorber 12 abuts the rubber ring 13.
In order to prevent invasion of the interior of the actuator by water droplets, the diameter of the holes 11a to 11c formed in the rubber cap 11 is smaller than the diameter of the lead wires 9a to 9c. Consequently, a troublesome work is required for the reading the lead wires 9a to 9c through the holes 11a to 11c. In addition, the watertightness of the housing 1 tends to be degraded due to reduction in the elasticity of the rubber cap as a result of a molecular change.